Multicollector mass spectrometers are well-known, particularly for distinguishing between isotopes. The detector array may be fixed or movable. Moreover, the distancing between detectors may be fixed within a moveable array. Flexibility of the mass spectrometer for dealing with ions of different types is a consideration in their design.
WO-97/15944 shows a multicollector mass spectrometer comprising a mass analyzer having a magnetic sector. A zoom lens is positioned in the path of the ion beam between the output of the mass analyzer and the collector array ion detectors. Where the spacing of the separated ions separated by the mass analyzer does not precisely match the spacing of the collector array, the zoom lens can provide a small adjustment as a correction.
EP-0952607 also describes an isotopic ratio mass spectrometer, comprising a mass analyzer having a magnetic sector. The detector arrangement, downstream from the mass analyzer, comprises a number of detectors. Each detector has a beam defining aperture positioned at the focal plane of the mass analyzer. For one of the detectors, a deflector is positioned downstream from the beam defining aperture and upstream from the collection electrode. The ion deflector comprises a pair of cylindrical electrodes with a radius, sector angle and applied potentials selected to deflect ions having the correct initial ion energy that passed through the slit at the entrance to the detector into the collection electrode.
U.S. Pat. No. 5,091,645 concerns a sector mass spectrometer, with two apertures located in its focal plane. The apertures are separated in a plane that is perpendicular to the sector analyzer's dispersive plane (also referred to as the analysing plane). An electrostatic deflector is placed upstream from the apertures to direct the ions selectively towards one of the apertures. In this way, the ion deflector acts along an axis that is perpendicular to the dispersive plane, so that it does not interfere with the mass-selective dispersion of the ions.
Also known is the Axiom mass spectrometer, originally manufactured by VG Elemental. In one option of this instrument, three large electron multiplier detectors were used, in view of their superior performance in comparison with smaller detectors. Three beam defining apertures were positioned in the focal plane of the mass analyzer, two of which were moveable. In order to disperse adjacent high mass beams more widely so as to make use of these large detectors, closely-spaced electrically-coupled deflector pins were placed just upstream of and were symmetrically disposed either side of the fixed central (axial) aperture. These were used to increase the separation of the beams adjacent the axial location. Between the symmetrically disposed pins, the central aperture accepted an undeflected ion beam through an earthed channel. Ion deflector plates were located downstream from the apertures to direct the ions passing through the outer two apertures towards the detectors.
All of these existing systems lack flexibility when dealing with ions with a range of different mass-to-charge-ratios, which is particularly desirable for isotopic ratio mass spectrometry. They also have difficulties in providing both high and low resolution mass spectra using the same instrument.